Steroid hormones have significant impact on the development and function of the nervous system and play crucial roles in various neurological and neuropsychiatric disorders. While steroids primarily act through the genomic mechanism by binding nuclear hormone receptors and activating transcription, accumulated evidence indicates that steroid hormones also induce biological effects rapidly and independent of their nuclear receptors. Despite the potential importance of such nongenomic steroid actions, their functional significance and underlying molecular mechanisms are still poorly understood. To address this gap in our knowledge, DopEcR, a recently discovered G-protein coupled receptor (GPCR), will be studied using genetic tools uniquely available in the fruit fly in Drosophila melanogaster. DopEcR is a strong candidate for a nonclassical steroid receptor, because this GPCR can directly bind and respond to the insect steroid hormone ecdysone as well as the catecholamine dopamine. Although DopEcR is known to have the highest sequence similarity with vertebrate -adrenergic receptors and is preferentially expressed in the nervous system, its function in intact animals is not known. The objective of this proposed research is to reveal the roles of DopEcR in behavioral regulation and identify its underlying mechanism of actions. The central hypothesis of this proposed research is that DopEcR-mediated ecdysone signaling plays a role in controlling balance of excitation and inhibition upon exposure to ethanol by modulating the effects of dopamine, cAMP and MAPK pathways. This hypothesis is based on my recent discovery that newly identified DopEcR mutants display intriguing phenotypes in ethanol-induced behaviors. The two specific aims that will be pursued in this project are: 1) Determine the endogenous expression patterns and functional sites of action of DopEcR, and 2) Determine the mechanisms by which DopEcR regulates behavioral responses to ethanol. For Aim 1, behavioral analyses will be carried out following the expression of wild type cDNA or RNAi for DopEcR in a neuronal subset-specific manner. For Aim 2, genetic variants of DopEcR will be examined for their interactions with dopamine, cAMP and MAPK pathways. Successful completion of these aims is expected to reveal how GPCR-mediated nongenomic steroid signaling controls ethanol-induced behavior in Drosophila. The outcomes of this application will have an important positive impact because they are expected to provide strong mechanism-based in vivo evidence for the nongenomic effects of steroid hormones on behavioral regulation. Due to the high functional and mechanistic conservation of steroid signaling and alcohol response behaviors, understanding these effects should provide novel insights into the future prevention and treatment of alcohol use disorders.